Coatings for implantable devices comprising poly(hydroxy-alkanoates) and diacid linkages

ABSTRACT

Coatings for an implantable medical device and a method of fabricating thereof are disclosed, the coatings include block-polymers comprising at least one poly(hydroxyacid) or poly(hydroxy-alkanoate) block, at least one block of a biologically compatible polymer and at least one type of linking moiety.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of application Ser. No. 10/902,982,filed Jul. 30, 2004, which is pending and which is incorporated hereinby reference.

FIELD

This invention is directed to coatings for drug delivery devices, suchas drug eluting vascular stents, and methods for producing the same.

DESCRIPTION OF THE STATE OF THE ART

Percutaneous transluminal coronary angioplasty (PTCA) is a procedure fortreating heart disease, which often manifests itself as stenoses incoronary arteries due to atherosclerosis. A surgeon inserts a catheterassembly having a balloon portion through the skin into a patient'scardiovascular system by way of the brachial or femoral artery. Thesurgeon positions the catheter assembly across the occlusive lesion. Thesurgeon inflates the balloon, once positioned, to a predetermined sizeto radially compress the atherosclerotic plaque of the lesion and toremodel the artery wall. After deflating the balloon, the surgeonwithdraws the catheter from the patient's vasculature.

But sometimes this procedure forms intimal flaps or tears arteriallinings. These injuries can collapse or occlude the vessel. Moreover,the artery may develop thrombosis and restenosis up to several monthsafter the procedure and may require further angioplasty or a surgicalby-pass operation. Implanting a stent into the artery can rectify theinjuries and help preserve vascular patency.

In a related manner, local administration of therapeutic agents withstents or stent coatings has reduced restenosis. But even with theprogress in stent technology in recent years, stents still can causeundesirable effects. For example, the continued exposure of a stent toblood can lead to thrombus formation itself, and the presence of a stentin a blood vessel can weaken the blood vessel wall over time, which mayallow arterial rupture or the formation of an aneurism. A stent can alsobecome so tissue overgrown that it becomes less useful and that itscontinued presence may cause a variety of problems or complications.Therefore, biodegradable or bioabsorbable stents are desirable todiminish risks that would otherwise associate with the continuedpresence of a no-longer-needed device at the treatment site.

Polymeric stent coatings can cause adverse and inflammatory reactions invivo. And there is much less history of using polymerically coatedstents, while bare metal stents have an extensive history. Use ofabsorbable or resorbable coatings also allows for drug release profilesthat are difficult to achieve with non-absorbable polymers. Hence, thereis great interest in using erodable, absorbable, or resorbable coatingson stents. Next, device coatings with non-fouling properties aredesirable. Non-fouling compounds such as poly(ethylene glycol) (PEG)provide these properties. But in order for a copolymer containing PEG topossess non-fouling properties, it is believed that the copolymer mustpresent a high concentration of PEG at the polymer-water interface—torepel protein because repelling proteins requires this. High PEGconcentration in the copolymer can deleteriously affect other coatingperformance aspects. For example, high PEG levels can significantlyincrease water swelling. This, in turn, can lead to too rapid drugrelease. It can also reduce the coating's mechanical properties,compromising its durability. Accordingly, there is a need fornon-fouling coatings based on biologically absorbable or biologicallydegradable polymers that are simultaneously non-fouling and that havethe drug release and mechanical properties suitable for a coating.

SUMMARY

Embodiments of the current invention relate to block copolymerscomprising a poly(hydroxyacid) or poly(hydroxy-alkanoate) block, a blockcomprising a biocompatible polymer, and a linking moiety.

In some embodiments, the poly(hydroxyacid) or poly(hydroxy-alkanoate)are chosen from specific compounds that are described below. Someembodiments select the biologically compatible polymer to bepoly(ethylene glycol) or other polymers that are described below.

Some embodiments select the linking moiety from dicarboxylic acids,diacid chlorides, anhydrides, or from a diisocyanate. In some cases thedicarboxylic acid is selected from specific compounds that are discussedbelow.

Invention block polymers can have the following formula

wherein A are poly(hydroxyacid) or poly(hydroxy-alkanoate) blocks, B areblocks of polymeric biocompatible moiety, X is a linking moiety, and nis an integer between about 2 and about 700.

In addition to polymer embodiments, embodiments of the current inventionare directed towards methods of making the polymers, coatings made fromthe polymers, and medical devices comprising those coatings.

DETAILED DESCRIPTION

The following definitions apply:

“Biologically degradable,” “biologically erodable,” “bioabsorbable,” and“bioresorbable” coatings or polymers mean those coatings or polymersthat can completely degrade or erode when exposed to bodily fluids suchas blood and that the body gradually resorbs, absorbs, or eliminates.The processes of breaking down, absorbing and eliminating the coating orpolymer occurs by hydrolysis, metabolic processes, enzymatic processes,bulk or surface degradation, etc.

For purposes of this disclosure “biologically degradable,” “biologicallyerodable,” “bioabsorbable,” and “bioresorbable” are usedinterchangeably.

“Biologically degradable,” “biologically erodable,” “bioabsorbable,” or“bioresorbable” stent coatings or polymers mean those coating that,after the degradation, erosion, absorption, or resorption processfinishes, no coating remains on the stent. “Degradable,”“biodegradable,” or “biologically degradable” broadly includebiologically degradable, biologically erodable, bioabsorbable, orbioresorbable coatings or polymers.

“Biodegradability,” “bioerodability,” “bioabsorbability,” and“bioresorbability” are those properties of the coating or polymer thatmake the coating or polymer biologically degradable, biologicallyerodable, or biologically absorbable, or biologically resorbable.

“Bulk degradation” and “bulk -degrading” refer to degradation processeswith several hallmarks. First, the water penetration rate into thepolymeric body of the stent or coating is much faster than the polymerhydrolysis or mass loss rate. Next, hydrolysis-induced reduction of thepolymer molecular weight occurs throughout the polymeric stent body orstent coating. Certain spatial variations in hydrolysis rate due to abuildup of acidic degradation products within the polymeric body canoccur and are termed the autocatalytic effect. The acidic degradationproducts themselves catalyze further polymer hydrolysis. The mass-lossphase typically occurs later in a bulk degradation process, after themolecular weight of the polymeric body has fallen. As a result, in anidealized bulk-degrading case, the stent or coating mass loss, occursthroughout the entire stent or the coating rather than just at thesurface.

The terms “block-copolymer” and “graft copolymer” are defined inaccordance with the terminology used by the International Union of Pureand Applied Chemistry (IUPAC). “Block-copolymer” refers to a copolymercontaining a linear arrangement of blocks. The block is defined as aportion of a polymer molecule in which the monomeric units have at leastone constitutional or configurational feature absent from the adjacentportions. “Graft copolymer” refers to a polymer composed ofmacromolecules with one or more species of block connected to the mainchain as side chains, these side chains having constitutional orconfigurational features that differ from those in the main chain.

The term “AB block-copolymer” is defined as a block-copolymer havingmoieties A and B arranged according to the general formula-{[A-]_(m)-[B]_(n)}—_(x), where each of “m,” “n,” and “x” is a positiveinteger, and m≧2, and n≧2.

The term “ABA block-copolymer” is defined as a block-copolymer havingmoieties A and B arranged according to the general formula-{[A-]_(m)-[B-]_(n)-[A]_(p)}-_(x), where each of “m,” “n,” “p,” and “x”is a positive integer, and m≧2, and n≧2, and p≧2.

The blocks of the ABA and AB block-copolymers need not be linked on theends, since the values of the integers determining the number of A and Bblocks are such as to ensure that the individual blocks are usually longenough to be considered polymers in their own right. Accordingly, theABA block copolymer can be named poly A-block-co-poly B block-co-poly Ablock-copolymer, and the AB block copolymer can be named polyA-block-co-poly B block-copolymer. Blocks “A” and “B,” typically, largerthan three-block size, can be alternating or random.

The term “poly(hydroxyacid)” refers to polymeric hydroxyacids.Hydroxy-acids are substances having at least one hydroxyl group ands atleast one carboxyl group.

The term “poly(hydroxy-alkanoate)” refers to polymerichydroxy-alkanoates. Hydroxy-alkanoates are esters of hydroxyacids.

A coating for an implantable medical device, such as a stent, accordingto embodiments of the present invention, can be a multi-layer structurethat can include any of the following four layers or layer combinations:

-   -   a primer layer;    -   a drug-polymer layer (also referred to as “reservoir” or        “reservoir layer”) or alternatively a polymer-free drug layer;    -   a topcoat layer; or    -   a finishing coat layer.

Each coating layer can be formed by dissolving the polymer or polymerblend in a solvent, or a solvent mixture, and applying that solution byspraying it onto the device or immersing the device into the solution.After this application, the coating dries by evaporation. Drying at anelevated temperature accelerates the process. The coating can beannealed between about 40° C. and about 150° C. for between about 5minutes and about 60 minutes. In some embodiments, annealing the coatingimproves its thermodynamic stability. Some embodiments requireannealing; some embodiments specifically exclude annealing.

To incorporate a drug into the reservoir layer, the drug can be combinedwith the polymer solution that is applied onto the device, as describedabove. Alternatively, a polymer-free reservoir can be made. Someembodiments desiring rapid drug release use polymer-free drugreservoirs. To fabricate a polymer free reservoir, the drug can bedissolved in a suitable solvent or mixture of solvents, and theresulting drug solution can be applied on the stent by spraying orimmersing the stent in the drug solution.

Alternatively, the drug can be introduced as a colloid system, such as asuspension in an appropriate solvent phase. Depending on a variety offactors, e.g., the nature of the drug, those having ordinary skill inthe art can select the suspension solvent the solvent phase of thesuspension, as well as the quantity of the drug to be dispersed in it.The suspension can be mixed with a polymer solution and the mixture canbe applied on the device as described above. The drug's suspension isapplied on the device without being mixed with the polymer solution.

The drug-polymer layer can be applied directly onto at least part of thedevice surface to store at least one active agent or a drug that isincorporated into the reservoir layer. The optional primer layer can beapplied between the device and the reservoir. In some embodiments, thisimproves the adhesion of the drug-polymer layer to the device. Theoptional topcoat layer can be applied over at least a portion of thereservoir layer and can serve as a rate limiting membrane, which helpsto control the drug release rate. In one embodiment, the topcoat layercan be essentially free from active agents or drugs. If a topcoat layeris used, the optional finishing coat layer can be applied over at leasta portion of the topcoat layer for further control of the drug releaserate and for improving coating biocompatibility. Without a topcoatlayer, the finishing coat layer can be deposited directly on thereservoir layer.

Release of a drug from a coating having both topcoat and finishing coatlayers includes at least three steps. First, the polymer of the topcoatlayer absorbs a drug at the drug-polymer-topcoat-layer interface. Next,the drug diffuses through the free volume between the topcoat layermacromolecules. Next, the drug arrives at the topcoat-finishing layerinterface. Finally, the drug similarly diffuses through the finishingcoat layer, arrives at the finish coat layer's outer surface, and thesedesorb from it into the surrounding tissue or bloodstream. Consequently,topcoat and finishing coat layer combinations, if used, can serve as arate limiting barrier. The drug can be released through the degradation,dissolution, or erosion of the layer.

In one embodiment, any or all of the layers of the device coating, canbe made of a biologically degradable, erodable, absorbable, orresorbable polymer. In another embodiment, the outermost layer of thecoating can be limited to such a polymer.

To illustrate in more detail, in a coating having all four layersdescribed above (i.e., the primer, the reservoir layer, the topcoatlayer and the finishing coat layer), the outermost layer is thefinishing coat layer, which is made of a polymer that is biologicallydegradable, erodable, absorbable, or resorbable. In this case, theremaining layers (i.e., the primer, the reservoir layer, the topcoatlayer) can also comprise a biologically degradable polymer, which can bethe same or different in each layer.

If a finishing coat layer is not used, the topcoat layer can be theoutermost layer and can be made of a biologically degradable polymer. Inthese or other embodiments, the remaining layers (i.e., the primer andthe reservoir layer) can also comprise a biologically degradablepolymer, which can be the same or different in each of the three layers.

If neither a finishing coat layer nor a topcoat layer is used, thedevice coating may have only two layers, the primer, and the reservoir.The reservoir in this case is the outermost layer of the device coatingand can comprise biologically degradable polymer. Optionally, the primercan also comprise a biologically degradable polymer. The two layers cancomprise the same or different materials.

The biological degradation, erosion, absorption or resorption of abiologically degradable, erodable, absorbable or resorbable polymer canincrease the drug release rate due to the gradual disappearance of thereservoir polymer, the topcoat layer, or both. Whether the release rateincreases depends on the drug release rate versus the polymerdegradation, erosion, and adsorption or resorption rate. By choosing anappropriate polymer, drug-to-polymer ratio, or concentration, andcoating design, the coating can provide either fast or slow drugrelease, as desired. By choice of the PEG or hydrophilic componentcontent, the hydroxy acid ester bond lability, the polymer molecularweight, in coating design, the polymer can be engineered to show fast orslow degradation. Those having ordinary skill in the art can determinewhether a coating having slow or fast release rate is advisable for aparticular drug. For example, fast release may be recommended forcoatings loaded with antimigratory drugs, which often need to bereleased within 1 to 2 weeks. For antiproliferative drugs, slow releasemay be needed (up to 30 days release time).

Biologically degradable, erodable, absorbable, or resorbable polymersthat can be used for making any of the stent coating layers include atleast one of poly(hydroxyacids), or derivatives thereof, such aspoly(hydroxy-alkanoates), or any combination thereof. Examples ofpoly(hydroxyacids) include any of poly(lactic acids), i.e.,poly(D,L-lactic acid) (DLPLA), poly(D-lactic acid), poly(L-lactic acid),poly(L-lactide), poly(D-lactide), poly(D,L-lactide), poly(caprolactone),poly(β-butyrolactone), poly(valerolactone), poly(glycolide),poly(3-hydroxyvaleric acid β-lactone), and poly(dioxanone). Someembodiments specifically exclude any one of or any combination of thesepoly(hydroxyacids).

Poly(lactic acid), H—[O—CH(CH₃)—C(O)]_(n)—OH, can be obtained byring-opening polymerization of lactide (a cyclic dimer of lactic acid),as demonstrated schematically by Reaction I, where lactide is compound(A) and poly(lactic acid) is compound (B):

The number average molecular weight of poly(lactides) can be betweenabout 5,000 and about 300,000 Daltons, corresponding to the value of theinteger n in the compound (B) between about 69 and about 4,166. Thosehaving ordinary skill in the art can determine the conditions underwhich the transformation of lactide to poly(lactide) illustrated byReaction I can be carried out.

Polymers including poly(hydroxyacid) or poly(hydroxy-alkanoate) moietiesthat can be used include block-copolymers illustrated by Formula I:

wherein A are blocks of a poly(hydroxyacids) or apoly(hydroxy-alkanoate), B are blocks of a polymeric biocompatiblemoiety, X is a linking moiety, and n is an integer having a valuebetween about 1 and about 880, such as, about 2 and about 350, or about4 and about 175.

A-Blocks

The number average molecular weight of a poly(hydroxyacid) orpoly(hydroxy-alkanoate) A-blocks can be between about 72 and about100,000 Daltons, more narrowly, between about 360 and about 30,000Daltons, or about 1000 Daltons.

Instead of poly(lactides), other poly(hydroxyacid) orpoly(hydroxyalkanoate) A-blocks can compose the block-copolymer ofFormula I. Examples of some of the poly(hydroxy-alkanoates) that can beused for making the alternative A-blocks include:

-   -   poly(3- or 4-hydroxybutyrate) (3-PHB or 4-PHB);    -   poly(3-hydroxyvalerate) (3-PHV);    -   poly(3-hydroxybutyrate-co-valerate) (3-PHB-3-HV);    -   poly(caprolactone) (PCL);    -   poly(lactide-co-glycolide) (PLGA);    -   poly(L-lactide);    -   poly(D-lactide);    -   poly(D,L-lactide);    -   poly(L-lactide-co-glycolide);    -   poly(D,L-lactide-co-glycolide);    -   poly(L-lactide-co-caprolactone);    -   poly(D,L-lactide-co-caprolactone);    -   poly(glycolide-co-caprolactone);    -   poly(L-lactide-co-D,L-lactide);    -   poly(L-lactide-co-trimethylene carbonate);    -   poly(D,L-lactide-co-trimethylene carbonate);    -   poly(glycolide-co-trimethylene carbonate);    -   poly(L-lactic acid);    -   poly(D-lactic acid); or    -   poly(D,L-lactic acid)

Any mixture of compounds of the groups described above can be also used.In some embodiments, these compounds are selected such that they excludeany one or any combination of the groups described above.

B. B-Blocks

B-blocks are biologically compatible polymers. Examples of suitablebiocompatible moieties include:

-   -   poly(alkylene glycols), for example, PEG,        poly(L-lysine)-graft-co-poly(ethylene glycol), poly(ethylene        oxide), polypropylene glycol) (PPG), poly(tetramethylene        glycol), or poly(ethylene oxide-co-propylene oxide);    -   poly(N-vinyl pyrrolidone);    -   polyacrylamide methyl propane sulfonic acid) (AMPS) and salts        thereof;    -   poly(styrene sulfonate);    -   sulfonated dextran;    -   polyphosphazenes;    -   poly(orthoesters);    -   poly(tyrosine carbonate);    -   hyaluronic acid and derivatives thereof, for example, hyaluronic        acid having a stearoyl or palmitoyl substitutent group,        copolymers of PEG with hyaluronic acid or with hyaluronic        acid-stearoyl, or with hyaluronic acid-palmitoyl;    -   heparin and derivatives thereof, for example, copolymers of PEG        with heparin; or copolymers thereof;    -   poly(2-hydroxyethyl methacrylate);    -   a graft copolymer of poly(L-lysine) and poly(ethylene glycol)        and mixtures thereof;    -   poly(2-hydroxyethyl methacrylate);    -   poly(3-hydroxypropyl methacrylate); or    -   poly(3-hydroxypropyl methacrylamide).

Any mixture of the compounds of these groups can be also used. Someembodiments select these compounds such that any one or any combinationof these groups or compounds is specifically excluded.

In some embodiments, the molecular weight of a suitable biocompatiblepolymeric moiety is chosen such that the patient's kidneys can clear thematerial from the patient's bloodstream. A molecular weight of asuitable biocompatible polymeric moiety can be below 40,000 Daltons toensure the renal clearance of the compound, or between about 100 andabout 40,000 Daltons, between about 300 and about 20,000 Daltons, orabout 1000 Daltons.

C. Linking Moiety X

The linking moiety X in block-copolymer (II) serves to connect twoadjacent interior poly(hydroxyacid) or poly(hydroxy-alkanoate) blocks.Moiety X can be derived from a dicarboxylic acid, (HOOC—(CH₂)_(y)—COOH),from its anhydride, from an acid chloride, from a diisocyanate, such ashexamethylene diisocyanate, 1,4-diisocyanatocyclohexane, or lysinediisocyanate, in which the carboxyl has been converted to an ester orother non-reactive group. One example of a dicarboxylic acid that can beused is succinic acid. Examples of some other dicarboxylic acids thatcan be used are summarized in Table 1.

TABLE I Dicarboxylic Acid (HOOC—(CH₂)_(y)—COOH) y Formula Name 0HOOC—COOH oxalic (ethanedioic) acid 1 HOOC—CH₂—COOH malonic(propanedioic) 3 HOOC—(CH₂)₃—COOH glutaric (pentanedioic) acid 4HOOC—(CH₂)₄—COOH adipic (hexanedioic) acid 5 HOOC—(CH₂)₅—COOH pimelic(heptanedioic) acid 6 HOOC—(CH₂)₆—COOH suberic (octanedioic) acid 7HOOC—(CH₂)₇—COOH azelaic (nonanedioic acid) 8 HOOC—(CH₂)₈—COOH sebacic(decanedioic) acid 9 HOOC—(CH₂)₉—COOH nonane-1,9-dicarboxylic(undecanedioic) acid 10  HOOC—(CH₂)₁₀—COOH decane-1,10-dicarboxylic(dodecanedioic) acid 11  HOOC—(CH₂)₁₁—COOH brassylic (tridecanedioic)acid 12  HOOC—(CH₂)₁₂—COOH dodecane-1,12-dicarboxylic (tetradecanedioic)acid 13  HOOC—(CH₂)₁₃—COOH tridecane-1,13-dicarboxylic(pentadecanedioic) acid 14  HOOC—(CH₂)₁₄—COOH thapsic (hexadecanedioic)acid NA HOOC—(C₆H₄)—COOH terephthalic acid NA HOOC—(C₂H₂)—COOH fumaricacid NA HOOC—(C₂H₂)—COOH maleic acid NA HOOC—(CH₂COCH₂)—COOH1,3-acetonedicarboxylic acid

Any mixture of dicarboxylic acids shown in

Table I, or their anhydrides, can be also used. In some embodiments, thedicarboxylic acid is specifically selected to exclude any one or anycombination of the acids listed in

Table I.

Block-copolymer shown by Formula I can be synthesized by standardmethods known to those having ordinary skill in the art, for example,polycondensation of PEG with PLA, followed by reaction with adicarboxylic acid or anhydride, or acid chloride, or chloroanhydride.

One way of synthesizing a Formula I block-copolymer is a two-stepprocess, comprising, first, ring opening polymerization and, second, acoupling step. Ring opening polymerization comprises reacting lactidewith PEG, where PEG is used as a macroinitiator. Condensation can occurat an elevated reaction temperature (about 140° C.), neat or in asolvent, such as toluene, in the presence of stannous octanoate. to thisyields a hydroxyl-terminated, triblock-copolymer PLA-PEG-PLA. Couplingcomprises further reacting the PLA-PEG-PLA triblock-copolymer with adicarboxylic acid or anhydride to connect the chains. For example,succinic or adipic, acid or anhydride can be used as the dicarboxylicacid. Coupling can be carried out in the presence of a coupling agent,such as 1,3-dicyclohexylcarbodiimide (DCC). Instead of DCC,1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) can be used. Withcarbodiimides, a catalyst such as N-dimethylaminopyridine (DMAP),diazabicycloundecane (DBU),N-(methylpolystyrene)-4-(methylamino)pyridine, or 4-pyrrolidinopyridineis used in coupling. Instead of the dicarboxylic acid or anhydride, adiisocyanate or diacid chloride can be used.

In some embodiments, using succinic anhydride as an anhydride, theobtained block copolymer, as in Formula I, can obtained, in whichpoly(D,L-lactide) serves as A-blocks, poly(ethylene-glycol) as B-blocks,and the succinic-acid-derived group, —CO—(CH₂)₁2-COOH—, serves as thelinking moiety X. One possible structure of such a block-copolymer isshown by Formula II:

The block-copolymer shown by Formula II can have a total number-averagemolecular weight between about 2000 and about 200,000 Daltons, or about45,000 Daltons. The value of the integer m can be between about 2 andabout 700, or about 10. The value of the integer n can be between about2 and about 700, or about 10. The value of the integer x can be betweenabout 5 and about 100, or about 14. The value of the integer y can bebetween about 2 and about 700, or about 10. The value of the integer zcan be between about 2 and about 700, or about 10. The value of theinteger a can be between about 5 and about 100, or about 14. The valueof the integer b can be between about 2 and about 700, or about 10.

In these or other embodiments, instead of dicarboxylic acid oranhydride, a chloroanhydride of a dicarboxylic acid can be used in chainextending. For example, adipoyl, sebacyl, or terephthaloyl chloride canbe used. In this reaction, HCl, which is released as a by-product, canbe neutralized to avoid hydrolyzing the PLA blocks. Common neutralizingagents are triethylamine and pyridine. Those having ordinary skill inthe art can determine how to neutralize HCl. In some embodiments, abromoanhydride of a dicarboxylic acid can be used in chain extending.

According to another embodiment of the present invention, the stepsequence can be reversed. Condensation can comprise reacting analpha-hydroxy acid, such as lactic acid, with a dicarboxylic acid oranhydride, to obtain a poly(lactic acid)-dicarboxylic acid adduct withcarboxyl end groups. Coupling comprises further reacting thePLA-dicarboxylic acid adduct with a hydroxy-terminated, biocompatiblemolecules such as PEG. Coupling can be carried out in the presence of acoupling agent, such as DCC or, alternatively, EDC, and a catalyst suchas DMAP. This scheme gives rise to a very similar multi-block copolymerwith the formula:

where the A and B blocks are defined as before.

According to yet another embodiment of the invention, a block copolymeris made wherein the poly(hydroxy acid) and polymeric, biocompatiblemoieties are reacted separately, and then coupled. Specifically, a firstblock is made by reacting a hydroxy-terminated polymeric, biocompatiblemoiety, such as PEG with a diacid or anhydride as shown below inReaction II.

A second block is made by ring opening polymerization with a cyclichydroxy-alkanoate, such as lactide, using a dihydric initiator, such as1,3-propanediol, as shown in Reaction III.

These two blocks are then coupled together using a coupling agent, suchas DCC or EDC, facilitated by a catalyst such as N-dimethylaminopyridine(DMAP), diazabicycloundecane (DBU),N-(methylpolystyrene)-4-(methylamino)pyridine, or 4-pyrrolidinopyridine.This embodiment may be described by Formula III, below:

wherein, A-blocks and B-blocks, and linking moiety X are as describedbefore. Linking moiety Y is a dihydric moiety that can be ethyleneglycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol,1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol,1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol,1,4-cyclohexanedimethanol, 1,4-hydroxymethylbenzene, serinol,dihydroxyacetone, any linear or branched C₂ to C₁₂ hydrocarbon with twoprimary hydroxyl groups, and any linear or branched C₂ to C₁₂ withunsaturation and two primary hydroxyl groups. In some embodiments, theY-moiety is selected to specifically exclude any one or any combinationof those listed above.

Any layer of the coating can contain any amount of the bioabsorbablepolymer(s) described above, or a blend of more than one such polymer. Ifless than 100% of the layer comprises a bioabsorbable polymer(s)described above, other, alternative, polymers can comprise the balance.Examples of the alternative polymers that can be used includepolyacrylates, such as poly(butyl methacrylate), poly(ethylmethacrylate), poly(ethyl methacrylate-co-butyl methacrylate),poly(acrylonitrile), poly(ethylene-co-methyl methacrylate),poly(acrylonitrile-co-styrene), and poly(cyanoacrylates); fluorinatedpolymers or copolymers, such as poly(vinylidene fluoride) andpoly(vinylidene fluoride-co-hexafluoro propene); poly(N-vinylpyrrolidone); polydioxanone; polyorthoester; polyanhydride;poly(L-lactide); poly(D,L-lactide); poly(D-lactide); poly(glycolide);poly(lactide-co-glycolide); poly(caprolactone); poly(-hydroxybutyrate);poly(-hydroxybutyrate); poly(3-hydroxybutyrate-co-3-hydroxyvalerate);poly(glycolic acid); poly(glycolic acid-co-trimethylene carbonate);polyphosphoester; polyphosphoester urethane; poly(amino acids);poly(trimethylene carbonate); poly(iminocarbonate);co-poly(ether-esters); polyalkylene oxalates; polyphosphazenes;biomolecules, such as fibrin, fibrinogen, cellulose, starch, collagenand hyaluronic acid; polyurethanes; silicones; polyesters; polyolefins;polyisobutylene and ethylene-alphaolefin copolymers; vinyl halidepolymers and copolymers, such as polyvinyl chloride; polyvinyl ethers,such as polyvinyl methyl ether; polyvinylidene chloride; polyvinylketones; polyvinyl aromatics such as polystyrene; polyvinyl esters suchas polyvinyl acetate; copolymers of vinyl monomers with each other andolefins, e.g., poly(ethylene-co-vinyl alcohol) (EVAL); ABS resins; andpoly(ethylene-co-vinyl acetate); polyamides such as Nylon 66 andpolycaprolactam; alkyd resins; polycarbonates; polyoxymethylenes;polyimides; polyethers, epoxy resins; polyurethanes; rayon;rayon-triacetate; cellulose; cellulose acetate; cellulose butyrate;cellulose acetate butyrate; cellophane; cellulose nitrate; cellulosepropionate; cellulose ethers; and carboxymethyl cellulose. Someembodiments select the alternate polymers to specifically exclude anyone or any combination of the alternate polymers listed above.

Representative examples of some solvents suitable for making the stentcoatings include N,N-dimethylacetamide (DMAC), N,N-dimethylformamide(DMF), tetrahydrofuran (THF), cyclohexanone, xylene, toluene, acetone,i-propanol, methyl ethyl ketone, propylene glycol monomethyl ether,methyl butyl ketone, ethyl acetate, n-butyl acetate, and dioxane. Somesolvent mixtures can be used as well. Representative examples of themixtures include:

-   -   DMAC and methanol (e.g., a 50:50 by mass mixture);    -   water, i-propanol, and DMAC (e.g., a 10:3:87 by mass mixture);    -   i-propanol, and DMAC (e.g., 80:20, 50:50, or 20:80 by mass        mixtures);    -   acetone and cyclohexanone (e.g., 80:20, 50:50, or 20:80 by mass        mixtures);    -   acetone and xylene (e.g. a 50:50 by mass mixture);    -   acetone, FLUX REMOVER AMS, and xylene (e.g., a 10:50:40 by mass        mixture); and    -   1,1,2-trichloroethane and chloroform (e.g., an 80:20 by mass        mixture).

FLUX REMOVER AMS is trade name of a solvent manufactured by Tech Spray,Inc. of Amarillo, Tex. comprising about 93.7% of a mixture of3,3-dichloro-1,1,1,2,2-pentafluoropropane and1,3-dichloro-1,1,2,2,3-pentafluoropropane, and the balance of methanol,with trace amounts of nitromethane. Those having ordinary skill in theart will select the solvent or a mixture of solvents suitable for aparticular polymer being dissolved.

Some embodiments comprise invention polymers coated onto a medicaldevice containing or constructed from a polymer, a medical devicecontaining or constructed from a metal, or a bare medical device, orinvention polymers coated on top of drug coatings already present on amedical device. Alternatively, some embodiments comprise inventionpolymers disposed between a medical device and a drug coating. Also,some embodiments comprise invention polymers composing polymer-basedmedical devices or invention polymers composing medical devicesubstrates (implantable or not). Some invention embodiments comprisemedical devices not made from polymer-containing or -constructed stents.Some invention embodiments comprise stents not made frommetal-containing or constructed stents.

In some embodiments, invention polymers serve as the base material forcoatings on medical devices. In some embodiments, coatings may contain aprimer layer. Some embodiments exclude a primer layer. In someembodiments, invention polymers serve as a topcoat on drug reservoirlayers either that contain or do not contain polymers. Some embodimentsemploy an additional polymer layer on top of the invention polymer. Thistop layer can be another layer of inventive polymer, a typical plasmapolymerized layer, a layer polymerized without a plasma source, or anycombination of these. Of these embodiments, some specifically excludelayers of additional inventive polymers, typical plasma polymerizedlayers, layers polymerized without a plasma source, or any combinationof these.

Some embodiments add conventional drugs, such as small, hydrophobicdrugs, to invention polymers (as discussed in any of the embodiments,above), making them biostable, drug systems. Some embodiments graft-onconventional drugs or mix conventional drugs with invention polymers.Invention polymers can serve as base or topcoat layers for biobeneficialpolymer layers. In some embodiments, a drug is any substance capable ofexerting a therapeutic, diagnostic, or prophylactic effect in a patient.

The selected drugs can inhibit vascular, smooth muscle cell activity.More specifically, the drug activity can aim at inhibiting abnormal orinappropriate migration or proliferation of smooth muscle cells toprevent, inhibit, reduce, or treat restenosis. The drug can also includeany substance capable of exerting a therapeutic or prophylactic effectin the practice of the present invention. Examples of such active agentsinclude antiproliferative, antineoplastic, antiinflammatory,antiplatelet, anticoagulant, antifibrin, antithrombin, antimitotic,antibiotic, and antioxidant substances, as well as their combinations,and any prodrugs, metabolites, analogs, congeners, derivatives, saltsand their combinations.

An example of an antiproliferative substance is actinomycin D, orderivatives and analogs thereof (manufactured by Sigma-Aldrich 1001 WestSaint Paul Avenue, Milwaukee, Wis. 53233; or COSMEGEN available fromMerck). Synonyms of actinomycin D include dactinomycin, actinomycin IV,actinomycin I1, actinomycin X1, and actinomycin C1. Examples ofantineoplastics include paclitaxel and docetaxel. Examples ofantiplatelets, anticoagulants, antifibrins, and antithrombins includeaspirin, sodium heparin, low molecular weight heparin, hirudin,argatroban, forskolin, vapiprost, prostacyclin and prostacyclin analogs,dextran, D-phe-pro-arg-chloromethylketone (synthetic antithrombin),dipyridamole, glycoprotein IIb/IIIa platelet membrane receptorantagonist, recombinant hirudin, thrombin inhibitor (available fromBiogen), and 7E-3B® (an antiplatelet drug from Centocor). Examples ofantimitotic agents include methotrexate, azathioprine, vincristine,vinblastine, fluorouracil, adriamycin, and mutamycin. Examples ofcytostatic or antiproliferative agents include angiopeptin (asomatostatin analog from Ibsen), angiotensin converting enzymeinhibitors such as CAPTOPRIL (available from Squibb), CILAZAPRIL(available from Hoffman-LaRoche), or LISINOPRIL (available from Merck &Co., Whitehouse Station, N.J.), calcium channel blockers (such asNifedipine), colchicine, fibroblast growth factor (FGF) antagonists,histamine antagonist, LOVASTATIN (an inhibitor of HMG-CoA reductase, acholesterol lowering drug from Merck &Co.), monoclonal antibodies (suchas PDGF receptors), nitroprusside, phosphodiesterase inhibitors,prostaglandin inhibitor (available from Glazo), Seramin (a PDGFantagonist), serotonin blockers, thioprotease inhibitors,triazolopyrimidine (a PDGF antagonist), and nitric oxide. Other usefuldrugs may include alpha-interferon, genetically engineered epithelialcells, dexamethasone, estradiol, clobetasol propionate, cisplatin,insulin sensitizers, receptor tyrosine kinase inhibitors, andcarboplatin. Exposure of the composition to the drug should notadversely alter the drug's composition or characteristic. Accordingly,drug containing embodiments choose drugs that are compatible with thecomposition. Rapamycin is a suitable drug. Additionally,40-O-(2-hydroxy)ethyl-rapamycin, or a functional analog or structuralderivative thereof, is suitable, as well. Examples of analogs orderivatives of 40-O-(2-hydroxy)ethyl-rapamycin include, among others,40-O-(3-hydroxy)propyl-rapamycin and40-O-2-(2-hydroxy)ethoxyethyl-rapamycin. Those of ordinary skill in theart know of various methods and coatings for advantageously controllingthe release rate of drugs, such as 40-O-(2-hydroxy)ethyl-rapamycin.

Some embodiments choose the drug such that it does not contain at leastone of or any combination of antiproliferative, antineoplastic,antiinflammatory, antiplatelet, anticoagulant, antifibrin, antithrombin,antimitotic, antibiotic, or antioxidant substances, or any prodrugs,metabolites, analogs, congeners, derivatives, salts or theircombinations.

Some invention embodiments choose the drug such that it does not containat least one of or any combination of actinomycin D, derivatives andanalogs of Actinomycin D, dactinomycin, actinomycin IV, actinomycin I1,actinomycin X1, actinomycin C1, paclitaxel, docetaxel, aspirin, sodiumheparin, low molecular weight heparin, hirudin, argatroban, forskolin,vapiprost, prostacyclin, prostacyclin analogs, dextran,D-phe-pro-arg-chloromethylketone (synthetic antithrombin), dipyridamole,glycoprotein IIb/IIIa platelet membrane receptor antagonist, recombinanthirudin, thrombin inhibitor and 7E-3B, methotrexate, azathioprine,vincristine, vinblastine, fluorouracil, adriamycin, mutamycin,angiopeptin, angiotensin converting enzyme inhibitors, CAPTOPRIL,CILAZAPRIL, or LISINOPRIL, calcium channel blockers, Nifedipine,colchicine, fibroblast growth factor (FGF) antagonists, histamineantagonist, LOVASTATIN, monoclonal antibodies, PDGF receptors,nitroprusside, phosphodiesterase inhibitors, prostaglandin inhibitor,Seramin, PDGF antagonists, serotonin blockers, thioprotease inhibitors,triazolopyrimidine, nitric oxide, alpha-interferon, geneticallyengineered epithelial cells, dexamethasone, estradiol, clobetasolpropionate, cisplatin, insulin sensitizers, receptor tyrosine kinaseinhibitors, carboplatin, Rapamycin, 40-O-(2-hydroxy)ethyl-rapamycin, ora functional analogs of 40-O-(2-hydroxy)ethyl-rapamycin, structuralderivative of 40-O-(2-hydroxy)ethyl-rapamycin,40-O-(3-hydroxy)propyl-rapamycin, and40-O-2-(2-hydroxy)ethoxyethyl-rapamycin, or any prodrugs, metabolites,analogs, congeners, derivatives, salts or their combinations.

Some invention embodiments comprise a drug or drug combination, and somerequire a drug or combination of drugs. Of the drugs specifically listedabove, some invention embodiments exclude a single or any combination ofthese drugs.

Some embodiments comprise invention polymers combined with otherpolymers in multilayer arrangements. For example, an invention polymercould under- or over-lay another polymer such as a polymer coated on adevice, a medical device, an implantable medical device, or a stent. Insome embodiments, invention polymers do not underlay another polymer; inother embodiments, invention polymers must overlay another polymer.

Some invention embodiments define the genera of medical devices toexclude at least one of self-expandable stents, balloon-expandablestents, stent-grafts, grafts (e.g., aortic grafts), vascular grafts,artificial heart valves, cerebrospinal fluid shunts, pacemakerelectrodes, guidewires, ventricular assist devices, artificial hearts,cardiopulmonary by-pass circuits, blood oxygenators, or endocardialleads.

Some invention embodiments comprise multilayered structures in which aninvention polymer is present in one or more of the layers of themultilayered structure.

The drug-polymer layer can be applied directly onto at least a part ofthe medical device surface to serve as a reservoir for at least oneactive agent or a drug. An optional primer layer can be applied betweenthe device and the reservoir to improve polymer adhesion to the medicaldevice. Some embodiments apply the topcoat layer over at least a portionof the reservoir layer, and the topcoat layer serves as a rate limitingmembrane, which helps to control the rate of release of the drug.

Implantable medical devices are also within the scope of the invention.Examples of such implantable devices include stents, stent-grafts,grafts (e.g., aortic grafts), artificial heart valves, abdominal aorticaneurysm devices, cerebrospinal fluid shunts, pacemaker electrodes, andendocardial leads (e.g., FINELINE and ENDOTAK, available from GuidantCorporation). The underlying structure of the device can be of virtuallyany design. The device can be made of a metallic material or an alloysuch as, but not limited to, cobalt chromium alloy (ELGILOY), stainlesssteel (316L), “MP35N,” “MP2ON,” ELASTINITE (Nitinol), tantalum,nickel-titanium alloy, platinum-iridium alloy, gold, magnesium, orcombinations thereof. “MP35N” and “MP2ON” are trade names for alloys ofcobalt, nickel, chromium and molybdenum available from Standard PressSteel Co. of Jenkintown, Pa. “MP35N” consists of 35% cobalt, 35% nickel,20% chromium, and 10% molybdenum. “MP20N” consists of 50% cobalt, 20%nickel, 20% chromium, and 10% molybdenum.

EXAMPLES

The following examples are provided to further illustrate embodiments ofthe present invention.

Example 1

Synthesis of multi-block PEG300-Poly(D,L-lactide), 30/70 weight ratio,coupled by succinic acid.

To a 250 ml, three necked flask, equipped with magnetic stirring,vacuum, and argon purge is added PEG300 (37.5 gm (0.125 mole). Using anoil bath, the PEG is heated to 105° C., and stirred under vacuum for twohours to remove water. The flask is purged with argon, and D,L-lactide(76.94 g, 0.534 mole) is added, and vacuum applied with stirring foranother 30 minutes. After purging with argon, the flask is heated to140° C., and polymerization is initiated by adding 10.8 ml of a 5% (w/w)stannous-octanoate-dry-toluene solution. After stirring for 24 hours,the reaction solution is cooled and poured into 500 ml of cold methanolto precipitate the polymer. The polymer is washed withmethanol/petroleum ether and dried under vacuum. The triblock copolymerfrom above (25 g, 4.17×10⁻⁴ mole) and succinic anhydride (0.0417 g,4.17×10⁻⁴ mole) is dissolved in 200 ml of anhydrous dichloromethane. Tothis is added 1,3-dicyclohexylcarbodiimide (0.103 g, 5×10⁻⁴ mole) and4-dimethylaminopyridine (0.0012 g, 1×10⁻⁵ mole). After stirring at roomtemperature for 24 hours, the reaction solution is centrifuged toprecipitate dicyclohexylurea and the supernatant solution poured into150 ml of cold methanol to precipitate the polymer. After filtration,the polymer is washed with methanol/petroleum ether and dried undervacuum.

Example 2

Synthesis of multi-block PEG600-Poly(D,L-lactide), 10/90 weight ratio,coupled by hexamethylene diisocyanate.

To a 250 ml, three necked flask, equipped with magnetic stirring,vacuum, and argon purge is added PEG600 (12.5 gm (0.0208 mole). Using anoil bath, the PEG is heated to 105° C., and stirred under vacuum for twohours to remove water. The flask is purged with argon and D,L-lactide(109.4 g, 0.76 mole) is added, and the vacuum applied with stirring foranother 30 minutes. After purging with argon, the flask is heated to140° C., and polymerization initiated by addition of 15.4 ml of a 5%(w/w) solution of stannous octanoate in dry toluene. After stirring for24 hours, 1,6-diisocyanatohexane (10.13 g, 0.0602 mole) as a 10%solution in dry dimethylformamide is added and the solution stirred at140° C. for another hour. The reaction solution is cooled and pouredinto 500 ml of cold methanol to precipitate the polymer. The polymer iswashed with methanol/petroleum ether and dried under vacuum. Thetriblock copolymer from above (25 g, 4.17×10⁻⁴ mole) and succinicanhydride (0.0417 g, 4.17×10⁻⁴ mole) is dissolved in 200 ml of anhydrousdichloromethane. To this is added 1,3-dicyclohexylcarbodiimide (0.103 g,5×10⁻⁴ mole) and 4-dimethylaminopyridine (0.0012 g, 1×10⁻⁵ mole). Afterstirring at room temperature for 24 hours, the reaction solution iscentrifuged to precipitate dicyclohexylurea and the supernatant solutionpoured into 150 ml of cold methanol to precipitate the polymer. Afterfiltration, the polymer is washed with methanol/petroleum ether anddried under vacuum.

Example 3

Use of the polymer from example 1 as a biocompatible topcoat

A first composition can be prepared by mixing the following components:

-   -   about 2.0 mass% poly(D,L-lactide); and    -   the balance, acetone.

The first composition can be applied onto the surface of bare 12 mmsmall VISION stent (available from Guidant Corporation). The coating canbe sprayed and dried to form a primer layer. A spray coater can be usedhaving a 0.014 round nozzle maintained at ambient temperature with afeed pressure 2.5 psi (0.17 atm) and an atomization pressure of about 15psi (1.02 atm). About 20 pg of the coating can be applied at per onespray pass. Between the spray passes, the stent can be dried for about10 seconds in a flowing air stream at about 50° C. About 110 μg of wetcoating can be applied. The stents can be baked at about 80° C. forabout one hour, yielding a primer layer composed of approximately 100 μgof poly(D,L-lactide)

A second composition can be prepared by mixing the following components:

-   -   about 2.0 mass % poly(D,L-lactide);    -   about 1.0 mass % everolimus; and    -   the balance, a 50/50 blend (w/w) of acetone and 2-butanone.

The second composition can be applied onto the dried primer layer, usingthe same spraying technique and equipment used for applying the primerlayer, to form the drug-polymer layer. About 180 μg of wet coating canbe applied followed by drying and baking at about 50° C. for about 1hour, yielding a dry drug-polymer layer having solids content of about170 μg.

A third composition can be prepared by mixing the following components:

-   -   about 2.0 mass % the polymer of example 1; and    -   the balance, a 50/50 blend (w/w) of acetone and chloroform.

The third composition can be applied onto the dried drug-polymer layers,using the same spraying technique and equipment used for applying theprimer and drug-polymer layers, to form a topcoat layer. About 110 μg ofwet coating can be applied followed by drying and baking at about 50° C.for about 1 hour, yielding a dry topcoat layer having solids content ofabout 100 μg.

Example 4

Use of the polymer from example 1 as a drug/polymer reservoir coating

A first composition can be prepared by mixing the following components:

-   -   about 2.0 mass% poly(D,L-lactide); and    -   the balance, acetone.

The first composition can be applied onto the surface of bare 12 mmsmall VISION stent (available from Guidant Corporation). The coating canbe sprayed and dried to form a primer layer. A spray coater can be usedhaving a 0.014 round nozzle maintained at ambient temperature with afeed pressure 2.5 psi (0.17 atm) and an atomization pressure of about 15psi (1.02 atm). About 20 μg of the coating can be applied at per onespray pass. Between the spray passes, the stent can be dried for about10 seconds in a flowing air stream at about 50° C. About 110 pg of wetcoating can be applied. The stents can be baked at about 80° C. forabout one hour, yielding a primer layer composed of approximately 100 μgof poly(D,L-lactide)

A second composition can be prepared by mixing the following components:

-   -   about 2.0 mass % the polymer of example 2;    -   about 0.5%; paclitaxel    -   the balance, a 50/50 blend (w/w) of acetone and chloroform.

The second composition can be applied onto the dried primer layer, usingthe same spraying technique and equipment used for applying the primerlayer, to form the drug-polymer layer. About 150 μg of wet coating canbe applied followed by drying and baking at about 50° C. for about 1hour, yielding a dry drug-polymer layer having solids content of about140 μg.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications can be made without departing from theembodiments of this invention in its broader aspects and, therefore, theappended claims are to encompass within their scope all such changes andmodifications as fall within the true spirit and scope of theembodiments of this invention.

Additionally, various embodiments have been described above. Forconvenience's sake, combinations of aspects (such as monomer orinitiator type) composing invention embodiments have been listed in sucha way that one of ordinary skill in the art may read them exclusive ofeach other when they are not necessarily intended to be exclusive. But arecitation of an aspect for one embodiment is meant to disclose its usein all embodiments in which that aspect can be incorporated withoutundue experimentation. In like manner, a recitation of an aspect ascomposing part of an embodiment is a tacit recognition that asupplementary embodiment exists in which that aspect specificallyexcludes that aspect.

Moreover, some embodiments recite ranges. When this is done, it is meantto disclose the ranges as a range, and to disclose each and every pointwithin the range, including end points. For those embodiments thatdisclose a specific value or condition for an aspect, supplementaryembodiments exist that are otherwise identical, but that specificallyinclude the value or the conditions for the aspect.

What is claimed is:
 1. A polymer having the formula:

wherein: A are poly(hydroxyacid) or poly(hydroxy-alkanoate) blocks; B are blocks of a biologically compatible polymer; X is a linking moiety; and n is an integer between 2 and 700; wherein the linking moiety is derived from at least one of or any combination of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, brassylic acid, dodecane-1,12-dicarboxylic acid, tridecane-1,13-dicarboxylic acid, thapsic acid, fumaric acid, maleic acid, and 1,3-acetonedicarboxylic acid; wherein the biologically compatible polymer is poly(L-lysine)-graft-co-poly(ethylene glycol; and wherein the poly(hydroxyacid) or poly(hydroxy-alkanoate) is one of poly(lactide-co-glycolide); poly(L-lactide); poly(D-lactide); poly(D,L-lactide); poly(L-lactide-co-glycolide); poly(D,L-lactide-co-glycolide); poly(L-lactide-co-caprolactone); poly(D,L-lactide-co-caprolactone); poly(L-lactide-co-D,L-lactide); poly(L-lactide-co-trimethylene carbonate); poly(D,L-lactide-co-trimethylene carbonate); poly(L-lactic acid); poly(D-lactic acid); poly(D,L-lactic acid); or a combination thereof.
 2. The polymer of claim 1 wherein the poly(hydroxyacid) or poly(hydroxy-alkanoate) is one of poly(L-lactide); poly(D-lactide); poly(D,L-lactide); poly(L-lactide-co-D,L-lactide); poly(L-lactic acid); poly(D-lactic acid); poly(D,L-lactic acid); or a combination thereof.
 3. The polymer of claim 1 wherein the linking moiety is derived from at least one of or any combination of malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, brassylic acid, dodecane-1,12-dicarboxylic acid, tridecane-1,13-dicarboxylic acid, thapsic acid, fumaric acid, maleic acid, and 1,3-acetonedicarboxylic acid.
 4. The polymer of claim 1 wherein the linking moiety is derived from at least one of or any combination of glutaric acid, adipic acid, pimelic acid, brassylic acid, dodecane-1,12-dicarboxylic acid, tridecane-1,13-dicarboxylic acid, thapsic acid, fumaric acid, maleic acid, and 1,3-acetonedicarboxylic acid.
 5. The polymer of claim 1 wherein each A is a poly(D,L-lactide) block.
 6. The polymer of claim 5 wherein n is about
 10. 7. A method of making a polymer comprising: reacting at least one poly(hydroxyacid) or poly(hydroxy-alkanoate) with at least one chain extending compound that is derived from at least one of or any combination of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, brassylic acid, dodecand-1, 12-dicarboxylic acid, tridacane-1, 13-dicarboxlic acid, thapsic acid, fumaric acid, maleic acid, and 1,3-acetonedicarboxylic acid, such that an A-X-A block polymer is formed; and reacting the A-X-A block copolymer with a biologically compatible polymer such that a final block copolymer is formed having the formula:

wherein A are poly(hydroxyacid) or poly(hydroxy-alkanoate) blocks; B are blocks of the biologically compatible polymer; X is a linking moiety that corresponds to the chain extending compound; and n is an integer between 2 and 700; wherein the biologically compatible polymer is poly(L-lysine)-graft-co-poly(ethylene glycol); and wherein the poly(hydroxyacid) or poly(hydroxy-alkanoate) is one of poly(lactide-co-glycolide); poly(L-lactide); poly(D-lactide); poly(D,L-lactide); poly(L-lactide-co-glycolide); poly(D,L-lactide-co-glycolide); poly(L-lactide-co-caprolactone); poly(D,L-lactide-co-caprolactone); poly(L-lactide-co-D,L-lactide); poly(L-lactide-co-trimethylene carbonate); poly(D,L-lactide-co-trimethylene carbonate); poly(L-lactic acid); poly(D-lactic acid); poly(D,L-lactic acid); or any combination of these.
 8. The method of claim 7 further comprising: depositing the final block copolymer on a region of an implantable portion of a medical device.
 9. The method of claim 8 wherein the medical device is a stent.
 10. The method of claim 7 wherein the poly(hydroxyacid) or poly(hydroxy-alkanoate) is one of a poly(lactide), poly(lactic acid), poly(lactide-co-glycolide), or a mixture thereof.
 11. The method of claim 7 wherein the chain extending compound is a dicarboxylic acid, diacid chloride, an anhydride, or a diisocyanate.
 12. The method of claim 7 wherein the chain extending compound is one of or any combination of oxalic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, nonane-1,9-dicarboxylic acid, decane-1,10-dicarboxylic acid, brassylic acid, dodecane-1,12-dicarboxylic acid, tridecane-1,13-dicarboxylic acid, thapsic acid, terephthalic acid, fumaric acid, maleic acid, and 1,3-acetonedicarboxylic acid.
 13. A coating made with the polymer of claim
 1. 14. A coating made with the polymer of claim
 2. 15. A coating made with the polymer of claim
 4. 16. A coating made with the polymer of claim
 5. 17. A medical device comprising the coating of claim
 13. 18. A medical device comprising the coating of claim
 14. 19. A medical device comprising the coating of claim
 15. 20. A medical device comprising the coating of claim
 16. 